Replacing the headlight bulbs on a Lexus GS300 is more complicated than on most vehicles. Instead of simply opening the bonnet and reaching behind the headlamp assembly to replace the bulb, the GS300 requires you to raise the vehicle, remove the tire, loosen the wheel well cover, and replace the bulb through there. The GS300 has two headlight bulbs on each assembly, a high beam bulb and a low beam bulb. The high beams use 9005-type bulbs and the low beams use 9006-type bulbs.
Turn the GS300's engine off. Put on a pair of clean gloves and place the jack under the vehicle. Open the bonnet.
Raise the GS300 to a comfortable position and remove the lug nuts with the wheel wrench. Once the nuts are removed, remove the wheel cover with the wheel wrench and remove the tire from the vehicle.
Remove the two screws holding the wheel well cover in place and take the cover off. Use a socket wrench to remove the two headlamp assembly retaining bolts. Pull the wiring connector off the rear of the assembly and push the assembly forward.
Go to the front of the GS300 and pull the assembly out of the engine compartment. Rotate the GS300's bulb sockets counterclockwise and pull them off the assembly. Pull the bulb out of the socket and install the new bulbs. Place the sockets back into the assembly and rotate them clockwise to secure them.
Place the assembly back into the engine compartment and reconnect the wiring connector at the rear of the assembly. Crawl under the vehicle and reattach the two retaining bolts. Place the cover back onto the wheel well and reinstall the two screws. Reattach the tire and close the bonnet.